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It might sound ridiculous, but even something like power windows on a car that didn't usually have them can drive value way up. "It could be horsepower-related, it could be power-window related, it could be comfort-related," says Allen. "Back in the Fifties, Sixties, and Seventies, you could go order cars and make them very unique. If there's a Mustang that pulls up on the auction block and it's a "one of one" because it had some kind of unique option, it'll bring more money than any of the other ones."